Human digestive system is a tube running from mouth to anus. Its main function is to breakdown complex molecules present in the food which cannot be absorbed as such into smaller molecules. These molecules are absorbed across the walls of the tube and the absorbed food reaches each and every cell of the body where it is utilised for obtaining energy. (a) Name the glands present in the buccal cavity and write the components of food on which the secretion of these glands act upon. (b) Two organs have a sphincter muscle at their exit. Name them. (c) What will happen if: (i) mucus is not secreted by the gastric glands. (ii) Villi are absent in the small intestine. OR (c) "Bile juice does not contain any enzyme, yet it has important roles in digestion." Justify the statement.

(a) The glands present in the buccal cavity are the salivary glands. They secrete saliva, which contains the digestive enzyme salivary amylase. This enzyme acts upon starch (a complex carbohydrate) and breaks it down into simple sugars.

(b) The two organs that have a sphincter muscle at their exit are:

1. Stomach: The exit of food from the stomach into the small intestine is regulated by a sphincter muscle.
2. Anus: The exit of waste material from the body is regulated by the anal sphincter.

(c)

(i) If mucus is not secreted by the gastric glands: The mucus protects the inner lining of the stomach from the harmful action of the highly acidic hydrochloric acid ($HCl$). In its absence, the acid will erode and damage the stomach wall, leading to severe acidity, inflammation, and gastric ulcers.

(ii) If villi are absent in the small intestine: Villi increase the surface area for the absorption of digested food. Without them, the absorption of nutrients will be drastically reduced, leading to malnutrition, weight loss, and extreme weakness despite eating food.

OR

(c) Justification of the statement:

Although bile juice does not contain any digestive enzymes, it is indispensable for digestion due to two critical functions:

1. Neutralization and Alkalinity: The food arriving from the stomach is highly acidic. Pancreatic enzymes require an alkaline medium to function. Bile juice is alkaline and neutralizes the acid, making the food alkaline so that enzymes like trypsin and lipase can act.
2. Emulsification of Fats: Fats are present in the small intestine as large globules, which limits the surface area for lipase to act. Bile salts break these large globules down into smaller globules (emulsification), significantly increasing the efficiency of pancreatic lipase action.